We can add a drop shadow to any HTML element using the CSS property box-shadow. Here's how.
我们可以使用CSS属性box-shadow将阴影添加到任何HTML元素。 这是如何做。
添加基本投影 (Adding a Basic Drop Shadow)
Let's first set up some basic HTML elements to add our drop shadows to:
让我们首先设置一些基本HTML元素，以将阴影添加到：
<div id="box1" class="box">Box1</div>
<div id="box2" class="box">Box2</div>
<div id="box3" class="box">Box3</div>Then add some basic CSS:
然后添加一些基本CSS：
p {padding: 10px;
}
.box {padding: 20px;width: 50%;margin: 30px auto;background: #000;color: #fff;
}The result is just three black boxes that will be easy for us to add drop shadows to by calling their unique id's:
结果只有三个黑匣子，我们可以通过调用它们的唯一ID轻松添加阴影：
To add a basic drop shadow, let's use the box-shadow property on the Box 1:
要添加基本的阴影，请使用Box 1上的box-shadow属性：
/* offset-x | offset-y | color */
#box1 {box-shadow: 6px 12px yellow;
}We have 3 parameters here. The first 2 are, respectively, the x-offset and y-offset. They set the location of the drop shadow.
这里有3个参数。 前两个分别是x偏移和y偏移。 他们设置阴影的位置。
The offset is relative to the origin, which in HTML is always the top left corner of an element. A positive x-offset will move the shadow to the right, and a positive y-offset will move the shadow downwards.
偏移量是相对于原点的，原点在HTML中始终是元素的左上角。 正x偏移将阴影向右移动，正y偏移将阴影向下移动。
The third parameter is the color of your drop shadow.
第三个参数是投影的颜色。
Keep in mind that although we used <div> elements here, the box-shadow property can be applied to any other HTML element as well.
请记住，尽管我们在这里使用了<div>元素，但是box-shadow属性也可以应用于任何其他HTML元素。
添加模糊半径 (Adding a Blur Radius)
If we want the shadow to look a little more realistic, we will want to experiment with the blur-radius parameter.
如果我们希望阴影看起来更真实一些，我们将尝试使用blur-radius参数。
This parameter controls how much to blur the shadow such that it becomes bigger and lighter. Let's apply it to Box 2:
此参数控制模糊程度以使其变大和变亮的程度。 让我们将其应用于方框2：
/* offset-x | offset-y | blur-radius | color */
#box2 {box-shadow: 6px 12px 4px red;
}The value of 4px sets the radius of the blur to apply to our drop shadow.
4px的值设置模糊的半径以应用于我们的阴影。
添加传播半径 (Adding a Spread Radius)
If we want to control the size of the shadow, we can use the spread-radius parameter which controls how much a shadow grows or shrinks.
如果要控制阴影的大小，则可以使用spread-radius参数来控制阴影的增长或收缩程度。
Let's add a spread radius of 8px to Box 2:
让我们在框2中添加一个8px的展开半径：
/* offset-x | offset-y | blur-radius | spread-radius | color */
#box2 {box-shadow: 6px 12px 4px 8px red;
}Remember the order of these parameters!
记住这些参数的顺序！
在单个属性中组合多个阴影 (Combining Multiple Shadows in a Single Property)
If we want to get fancy, we can add multiple drop shadows to an element using a single box-shadow property.
如果想花哨的话，可以使用单个box-shadow属性为元素添加多个阴影。
Let's do that with Box 3 by simultaneously adding a blue and green drop shadow:
让我们在方框3中同时添加一个蓝色和绿色的阴影来做到这一点：
/* Any number of shadows, separated by commas */
#box3 {box-shadow: 6px 12px 2px 2px blue, -6px -12px 2px 2px green;
}奖励：创建插入阴影 (Bonus: Create an Inset Shadow)
While it will not create a drop shadow, the inset parameter can also be used with the box-shadow property.
尽管不会创建阴影，但inset参数也可以与box-shadow属性一起使用。
As the name suggests, this parameter creates an inset shadow (i.e. shadow inside a box).
顾名思义，此参数将创建插入阴影(即，框内的阴影)。
The inset parameter can be placed either at the beginning or the end of the box-shadow property. Here we demonstrate its use with a blockquote element.
可以将inset参数放在box-shadow属性的开头或结尾。 在这里，我们通过blockquote元素演示其用法。
HTML:
HTML：
<blockquote><q>The key to success is to start before you're ready.</q><p>— Marie Forleo</p>
</blockquote>CSS:
CSS：
blockquote {width: 50%;margin: 50px auto;padding: 20px;font-size: 24px;box-shadow: inset 10px 5px black;
}Of course you can add some blur and spread to enhance the shadow, or even multiple shadows:
当然，您可以添加一些模糊和散布以增强阴影，甚至多个阴影：
box-shadow: inset 10px 5px 25px 5px black, 5px 5px 12px 2px black;With the box-shadow property, we can easily make elements on a web page stand out to create a nice 3D lighting effect.
使用box-shadow属性，我们可以轻松地使网页上的元素突出以创建漂亮的3D照明效果。
If you want to do some experimenting yourself, here's a code pen I created with the examples used in this tutorial.
如果您想做一些实验，请使用我在本教程中使用的示例创建的一支代码笔 。
Play around and see what you can come up with!
玩转，看看你能想到什么！
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翻译自: https://www.freecodecamp.org/news/css-tutorial-drop-shadow/
